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Geomatics in Earthquake Mitigation

Ramanuj Banerjee, Devendra Kumar, K. K. Mohanty and Shailesh Nayak
ESHD/MWRG-RESA, Space Applications Centre (ISRO), Ahmedabad – 380015.

Abstract
The modern space-based remote sensing, spatial science and information technologies have opened up efficient means for tectonic studies and evaluation of earthquake risk and mitigation strategy. The areas affected by earthquake are large and generally confined to plate boundaries. Fault rupture and associated surface deformation, liquefaction, damage due to ground shaking can be observed using remote sensing. The measurement of fault displacements using Global Positioning System (GPS) and radar interferometry is useful to study co-seismic and post-seismic deformations. The monitoring of deformation indicates about strain built up. Liquefaction, which occurred during the Kachchh earthquake, was mapped using IRS data (WiFS, LISS-III and PAN). Seismic hazard zonation is essential for regional and urban planning and the only safeguard for earthquake. Seismic micro-zonation maps are derived from estimation of various effects of seismic waves at the terrain surface: ground shaking, surface faulting, liquefaction. GIS helps in analyzing large volume of data on active faults, geological structure, soil type, depth to groundwater table, topography and infrastructure. This article attempts to review the potential of geomatics as tool in earthquake mitigation.

Introduction
Natural disasters like cyclone, flood, drought, landslide, earthquake etc. have devastating effect on life and property. Earthquakes are short-lived, menacing and the most feared natural hazards because of their sudden impact and devastation in a matter of few seconds inflicting immense losses of life and property. Crustal deformation is in fact a direct manifestation of the process that leads to earthquakes. Though areas prone to seismic hazards are fairly well known, there has been very little advance in our ability to predict when, where, or with what magnitude will the next earthquake strike. Since we are not in a position to predict an earthquake, we must atleast try to find out the scientific causes that can lead to such catastrophic earthquakes. For this, study of neotectonics and geology of a particular region is very important. The major thrust is to arrive at a probabilistic zoning map of the study area based on basis of these scientific findings and incorporate all relevant details related to damage assessment, rescue and relief operations.

Geomatics is a recently emerging technology, which can play a vital role in mitigation of natural disasters. Geomatics is a conglomerate of measuring, mapping, geodesy, satellite positioning (GPS), photogrammetry, computer systems and computer graphics, remote sensing, geographic information systems (GIS) and environmental visualization. The earth observation satellites provide comprehensive, synoptic and multi-temporal coverage of large areas for a wide range of scales, from entire continents to details of a few meters in real time and at frequent intervals and thus have become valuable for continuous monitoring of earth and its atmosphere (Roy et al., 2000). Remote sensing and GIS based change detection technique is used to assess earthquake induced damages to houses and other structures accurately and speedily as this technique is cost effective, unbiased, and free from subjectivity, time saving and provides quantitative damage assessment.    Role of Geomatics in Tectonic Study
Lineaments and faults are the sources of neotectonic activities, which may often lead to an increase in seismic hazards of the region. LISS-III and panchromatic (PAN) merged images can be used to delineate vertical to high angle faults or suspected faults. All lineaments mapped from enhanced False Color Composite (FCC) and edge enhancement images can be merged to bring out the total lineament map of the area. Based on Mohr’s theory, failure criteria, and statistical analysis of remotely sensed lineament data, horizontal compressive stress values (SHmax) can be estimated (Sahoo et.al., 2000, Saraf et.al., 2002). Such compressive stress determination has been done for the Kachchh area after the Bhuj earthquake and they are found to match roughly with those provided by USGS sources (Maiti, 2001).

The drainage pattern is an excellent indicator of not only the surficial lithology and the geological structures but also the ongoing morphotectonic processes of the planet Earth. Among the various drainage patterns, the ‘eyed drainage’ pattern is considered to be one of the most significant anomalies and such mega-eyed drainage are found to signify ongoing tectonic movements (Ramasamy et.al., 2000). IRS-1A and IRS-1C FCC imagery (using blue, green and red colours in spectral ranges) can be interpreted with a specific look to bring out the eyed drainages.

Synthetic Aperture Radar (SAR) i.e. Space-borne interferometry, which gives high-resolution imagery of earthquake prone areas, accompanied by GPS survey provides an ability to identify subtle changes on Earth’s crust (Lunetta and Elvidge, 1999) and identification of non-homogenous surface deformation (co-seismic deformation). The displacement field of Landers earthquake, California (magnitude 7.3, 28th June 1992) has been computed using ERS-1 SAR data (Massonnet et al., 1993). Land subsidence case studies using D-InSAR techniques over parts of Germany, Italy and Mexico have also been reported. Similar use of D-InSAR technique has also been used to monitor Latur earthquake, 1993 wherein surface deformation of the order of 2.8cms could be mapped (Majumdar et al., 2002).

Geomatics in Seismic Zoning
Earthquake induced damage can occur due to liquefaction and or related phenomena, landslides, ground motion, tsunamis and seiches, ground rupture and tectonic subsidence or uplift. Seismic Zoning can be defined as delineation of geographic areas with varied potentials for surface faulting, ground shaking, liquefaction and landsliding during future earthquakes of specific size and location (Berlin, 1980). While seismic zoning takes into account the distribution of seismic hazard over the entire country or region, seismic micro-zonation takes into account the effect of local site conditions i.e. the detailed distribution of earthquake risk within each seismic zone. For seismic micro-zoning all data related to geology, ground acceleration, historical earthquake and remote sensing derived parameters are incorporated into a common spatial database and then analyzed to get the Hazard map. Such a study has been attempted for the Kachchh area (Gupta, 2002).

Liquefaction is one important aspect of seismic micro-zoning and refers to the loss of shearing resistance (when the effective stress reduces to zero) or the development of excessive strains resulting from transient or repeated disturbances of saturated unconsolidated fine cohesionless soils, leading to dramatic examples of damage. Liquefaction sensitivity index (LSeI) is useful for determining the relative liquefaction hazard potential and provide an index of possible maximum ground displacement. LSeI can be mapped using pre and post earthquake LISS-III and WiFS data sets (Ramakrishna et.al., 2003). Figure 1 shows a typical ground signature of liquefaction vis-a-vis that in remote sensing image.


Fig 1. (i) Ground evidence of liquefaction
(ii) IRS-WiFS Difference FCC of Kachchh showing spatial extent of liquefaction
(iii) LSeI in and around Bhuj

High revisit capabilities of IRS-WiFS images have been helpful in studying the persistence of the released water (water surges) i.e. liquefaction in near real time (Mohanty et.al., 2001). There was relative increase in the volume of water in the WiFS images of 29th January (Bhuj earthquake), which completely disappeared on 4th February 2001. Even liquefaction zone boundaries can be delineated or identified on remote sensing images like Landsat TM and MSS as has been done by Gupta et al., 1995 in the Bihar-Nepal region for the 1934 earthquake.

Micro-zonation study has been carried out in various earthquake-prone parts of the world including Memphis, Mexico, British Columbia, Puerto-Rico, City of Basel etc. It has also been observed that at many sites surface motions are influenced primarily by top 20-30 m of soil, so sediment cover (subsurface geology) has a role to play in earthquake and so 3-D subsurface map must be prepared. This can be done with help from GIS as has been attempted for the city of Delhi.    Geomatics in Damage Assessment
Disaster management consists of two main phases—disaster prevention and disaster preparedness (disaster relief, rehabilitation and reconstruction). In disaster prevention phase, GIS is used to manage the large volume of data needed for the hazard and risk assessment. In disaster preparedness phase, it is a tool for the planning of evacuation routes, for the design of centers for emergency operations, and for integration of satellite data with other relevant data in the design of disaster warning systems. High-resolution satellite imagery offers new possibilities for the earthquake damage assessment and thus multidisciplinary approach combining remote sensing techniques, spatial analysis and earthquake engineering can provide fast loss estimation. The information can be integrated into a GIS database and transferred via satellite networks or Internet to the rescue teams deployed on the affected zone. The results of a fast damage assessment received by the field operators could help the civil protection in order to co-ordinate the emergency operations (Chiroiu et al., 2001). Another disaster-based tool used in pre-disaster management is Vulnerability Mapping, which helps in possible mapping of liquefaction prone areas. Successful uses of remote sensing data have been made for damage assessment in the case of the 1995 Kobe, Japan and the 1999 Kocaeli, Turkey earthquakes (Matsuoka et al., 2000 & Estrada et al., 2000). Recently, military weather satellite DMSP of the U.S., using nighttime lights of the cities has been used to estimate the damaged areas (Kohiyama et al., 2000). Recently developed pseudo-colour transformation techniques (PCT) have been successfully evaluated on these same sets of pre-and post-earthquake datasets. The PCT image depicts liquefaction phenomenon in and around Ghandidham and Kandla that led to sinking of many buildings near Kandla port. Damage assessment of Bhuj earthquake has also been done using Landsat-7 Satellite images (Yusuf et.al., 2001). Even assessment or mapping of damages to homes and ground in water-affected regions during Bhuj quake using IRS-1C & 1D (PAN and LISS-III) pre-and post-earthquake datasets have also been attempted.

A new generation of high resolution optical satellites (IKONOS, TES, EROS etc) provide imagery with 1-meter resolution in panchromatic mode and 4 meters in multispectral. In the near future, less than 1m resolution of Quickbird satellite will be available for the civil applications (0.61 meters in panchromatic mode, 2.8 meters in multispectral). The high level of details makes possible reliable damage detection to the buildings or to other structures (Chiroiu et al., 2001). Figure 2 shows the use of remote sensing image for mapping of building damage due to earthquake (Chiroiu et al., 2001).


Fig 2. (a) Shows badly damaged buildings (red mark)
(c) Shows minor damages caused to buildings and apartments (yellow mark)

Role of Geomatics in Earthquake Forecasting
French micro-satellite DEMETER helps in detection of Electro-magnetic Emissions from earthquake regions, which can be used for earthquake prediction. It is known that the earth’s crust emits electromagnetic signals a few hours before an impending event, which affects the ionospheric electron density in turn. This can be detected may be in near future via the GSAT-2 satellite as it is proved that electromagnetic perturbations and seismic activity have a strong correlation with one another. Satellite thermal survey is a tool for investigations of seismoactive regions and earthquake predictions. The earth’s surface images obtained in the thermal IR part of the spectrum are generated due to surface temperature and this is very relevant for studies in seismoactive regions. The NOAA/AVHRR-series satellite thermal images (STI) study have showed the presence of positive anomalies (of the order of 2-3°C) of the outgoing Earth radiation flux recorded at night-time and associated with the largest linear structures and fault systems of the crust (Tronin, 2000). The IR anomalies occur in the weakest and consequently the most ‘sensitive’ crustal zones i.e. in the point of intersection of major crust faults. These thermal anomalies start appearing prior to the earthquake (7-24 days before) and fade out within a day or two after the quake has occurred. A study of the Central Asian seismoactive region actually gave the idea that there was a statistically significant correlation between the activity of IR anomalies (mean value of area per year or month) and seismic activity. However, none of the above indicators have been established conclusively to be used as earthquake precursors.
   Conclusion
Geomatics has potential use in various aspects of earthquake related studies such as active tectonics, hazard zonation and damage assessment and even act as possible precursors for earthquake. SRTM data, multi-spectral data, SAR data, IRS stereo data and aerial photos, allow us to map terrain properties, such as crustal deformation, thermal anomaly, geology etc, both temporally and spatially. SAR interferometry and GPS survey are the only avenues for mapping of deformation. High-resolution satellite data can be used in real-time damage assessment. GIS is a key for spatio-temporal analysis of earthquake data for hazard zonation and damage assessment. Remote Sensing and GIS provides a platform for gathering and organizing the information and hence proven their usefulness in disaster management. Geomatics can play a vital role in mitigation of natural hazards.

Acknowledgement
Authors would like to record their sincere thanks for Dr. K.L. Majumdar, Deputy Director, RESIPA/SAC and Dr. K.N. Shankara, Director, Space Applications Centre for supporting this study. The authors (Ramanuj Banerjee and Devendra Kumar) are indebted to CSIR (Council of Scientific and Industrial Research) for providing financial assistance in form of Junior Research fellowship.

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